1. Field of the Invention
A method and apparatus to form horizontal drainholes for in situ leach mining.
2. Description of the Prior Art
The prior art discloses several methods of forming drain wells from a main generally vertical hole. One example is the U.S. Pat. No. 4,222,611 to W. C. Larson et al wherein branch wells are whipstocked from a main vertical hole at an angle from about 2 degrees to 60 degrees. In other references, drainholes have been formed approximately 90 degrees from the vertical (e.g. U.S. Pat. No. 2,171,416 to R. E. Lee and U.S. Pat. No. 4,249,777 to W. C. Larson et al). Most of those inventions which utilize horizontal drainhole drilling have been used to improve the productivity of oil or gas wells. However, these horizontal holes have, to our knowledge, never been cased and perforated as would be required in an effective deep lying in situ leach mining operation. In Pat. No. 4,249,777 to our coinventor, W. C. Larson, horizontal branch wells were disclosed for an in situ leach mining method. Therein the drainhole drilling technique employs a flexible U-joint spiral reamer and a whipstock which is used to form the horizontal branches. The branches are also disclosed as being either cased or uncased. What is not disclosed or taught is the specific in situ leach mining method used to form horizontal drainholes in which a small radius hole (about 19 feet in the example disclosed) joins the horizontal hole to the deep generally vertical main hole. The present invention thus allow deep lying (in excess of 2,000 feet) thin beds, such as those bearing uranium ore, to be economically mined by the in situ leach mining method. The ASME publication 81-Pet-14 entitled "Technical Considerations in Drainhole Drilling," by D. R. Holbert provides excellent background material on drainholes.
The principles underlying this invention and several related inventions can be found in the final contract (JO199113) report entitled "Evaluation of Branch and Horizontal Boreholes for In Situ Leach Mining" prepared by Maurer Engineering Inc. of Houston, Texas, for the U.S. Bureau of Mines and first released for publication in January 1981.
The present invention seeks to overcome the deficiencies of the prior art by providing a novel method and the apparatus to practice that method which is used to form generally horizontal drainholes that are cased and perforated. It further seeks to use these drainholes with in situ mining methods and a casing which is perforated before being placed in the horizontal branch well.